Three Dimensional Diagnostic Ultrasonic Image Display

ABSTRACT

A three dimensional ultrasonic imaging system acquires 3D image data from a volumetric region and processes the image data to produce a live 3D image of the volumetric region, a 2D image of a face or a central cut plane of the volumetric region, and a 2D image of a cut plane which is orthogonal to the plane of the first 2D image. The two 2D images enable the user to quickly orient the position of the anatomy shown in 3D in the live 3D image.

This invention relates to ultrasonic diagnostic imaging and, inparticular, to the display of three dimensional images of a volumetricregion of a subject.

Live, real time 3D imaging has been commercially available for severalyears. Live 3D imaging, even more than standard 2D imaging, posestradeoffs of image quality versus frame rate. For good image quality itis desirable to transmit and receive a large number of well-focused scanlines over the image field. For high real time frame rate, particularlyuseful when imaging a moving object such as the heart, it is desirableto transmit and receive all of the scan lines for an image in a shortperiod of time. However, the transmission and reception of scan lines islimited by the laws of physics governing the speed of sound to 1540m/sec. Thus, depending upon the depth of the image (which determines thetime needed to wait for the return of the echoes over the full depth ofthe image), a determinable amount of time is required to transmit andreceive all of the scan lines for an image, which may cause the framerate of display to be unacceptably low. A solution to this problem is toreduce the number of scan lines and increase the degree of multilinereception. This will increase the frame rate, but possibly at theexpense of degradation in the image quality. In 3D imaging the problemis even more acute, as hundreds or thousands of scan lines may be neededto fully scan a volumetric region. Another solution which reduces thenumber of scan lines is to narrow the volume being scanned, which alsoincreases the frame rate. But this may undesirably provide only a viewof a small section of the anatomy which is the subject of the ultrasonicexam.

As previously mentioned, this dilemma presents itself most starkly whenimaging a moving object such as the beating heart. An ingenious solutionto the dilemma for 3D imaging of the heart is described in U.S. Pat. No.5,993,390. The approach taken in this patent is to divide the cardiaccycle into twelve phases. A region of the heart which is scanned duringone-twelfth of the cardiac cycle will produce a substantially stationary(unblurred) image. The inventors in the patent determined that nine suchregions comprise the full volume of the typical heart. Thus, the heartis scanned to acquire one of these nine subvolumes during each of thetwelve phases of the heart cycle. Over a period of nine heartbeats acomplete 3D image of the heart is pieced together from the subvolumesfor each of the twelve phases of the heart cycle. When the completeimages are displayed in real time in phase succession, the viewer ispresented with a real time image of the heart. This is a replayed image,however, and not a current live image of the heart. It would bedesirable to enable current live 3D imaging of a volumetric regionsufficient to encompass the heart.

In accordance with the principles of the present invention, current livesubvolumes of the heart are acquired in real time. The subvolumes can besteered over a maximum volumetric region while the ultrasound probe isheld stationary at a chosen acoustic window. This enables the user tofind the best acoustic region for viewing the maximum volumetric region,then to interrogate the region by steering live 3D subvolumes over it.In one embodiment the subvolumes are steerable over predeterminedincremental positions. In another embodiment the subvolumes arecontinuously steerable over the maximum volumetric region. A firstdisplay embodiment is described with concurrent 3D and 2D images thatenable the user to intuitively sense the location of the subvolume.Another display embodiment is described which enables the user to selectfrom among a number of desirable viewing orientations.

In the drawings:

FIG. 1 illustrates an ultrasonic diagnostic imaging system constructedin accordance with the principles of the present invention.

FIG. 2 illustrates in block diagram form the architecture of anultrasound system constructed in accordance with the principles of thepresent invention.

FIG. 3 illustrates in block diagram form the major elements of a 3Dprobe and beamformer in one embodiment of the present invention.

FIG. 4 illustrates a volumetric region which can be scanned from atwo-dimensional matrix transducer.

FIG. 5 illustrates a volumetric region encompassing the heart in anapical view.

FIG. 6 illustrates the division of the volumetric region of FIGS. 4 and5 into three subvolumes.

FIG. 7 illustrates elevation planes of the subvolumes of FIG. 6.

FIGS. 8 a-8 c are ultrasonic images of the three subvolumes of FIG. 6.

FIGS. 9 a-9 c illustrate the beam plane inclination used to scan thethree subvolumes of FIGS. 8 a-8 c.

FIG. 10 illustrates the multiline reception used in the acquisition ofthe three subvolumes of FIGS. 8 a-8 c.

FIGS. 11-22 are screen shots of two and three dimensional images indifferent orientations in accordance with the present invention; and

FIGS. 11 a-22 a illustrate the views of the heart which may be obtainedwith the image orientations of FIGS. 11-22.

FIG. 23 is a block diagram illustrating the control sequence forcontinuous steering of a subvolume over a maximum volumetric region.

FIG. 24 illustrates a subvolume repositioned by continuous steering.

Referring first to FIG. 1, an ultrasound system constructed inaccordance with the principles of the present invention is shown. Theultrasound system includes a mainframe or chassis 60 containing most ofthe electronic circuitry for the system. The chassis 60 is wheel-mountedfor portability. An image display 62 is mounted on the chassis 60.Different imaging probes may be plugged into three connectors 64 on thechassis. The chassis 60 includes a control panel with a keyboard andcontrols, generally indicated by reference numeral 66, by which asonographer operates the ultrasound system and enters information aboutthe patient or the type of examination that is being conducted. At theback of the control panel 66 is a touchscreen display 68 on whichprogrammable softkeys are displayed for specific control function asdescribed below. The sonographer selects a softkey on the touchscreendisplay 18 simply by touching the image of the softkey on the display.At the bottom of the touchscreen display is a row of buttons, thefunctionality of which varies in accordance with the softkey labels onthe touchscreen immediately above each button.

A block diagram of the major elements of an ultrasound system of thepresent invention is shown in FIG. 2. An ultrasound transmitter 10 iscoupled through a transmit/receive (T/R) switch 12 to a transducer array14. Transducer array 14 is a two-dimensional array (matrix array) oftransducer elements for performing three-dimensional scanning. Thetransducer array 14 transmits ultrasound energy into a volumetric regionbeing imaged and receives reflected ultrasound energy, or echoes, fromvarious structures and organs within the region. The transmitter 10includes a transmit beamformer which controls the delay timing by whichthe signals applied to elements of the transducer array are timed totransmit beams of a desired steering direction and focus. Byappropriately delaying the pulses applied to each transducer element bytransmitter 10, the transmitter 10 transmits a focused ultrasound beamalong a desired transmit scan line. The transducer array 14 is coupledthrough T/R switch 12 to an ultrasound receiver 16. Reflected ultrasoundenergy from points within the volumetric region is received by thetransducer elements at different times. The transducer elements convertthe received ultrasound energy to received electrical signals which areamplified by receiver 16 and supplied to a receive beamformer 20. Thesignals from each transducer element are individually delayed and thenare summed by the beamformer 20 to provide a beamformed signal that is arepresentation of the reflected ultrasound energy level along points ona given receive scan line. As known in the art, the delays applied tothe received signals may be varied during reception of ultrasound energyto effect dynamic focusing. The process is repeated for multiple scanlines to directed throughout the volumetric region to provide signalsfor generating an image of the volumetric region. Because the transducerarray is two-dimensional, the receive scan lines can be steered inazimuth and in elevation to form a three-dimensional scan pattern. Thebeamformed signals may undergo signal processing such as filtering andDoppler processing and are stored in an image data buffer 28 whichstores image data for different volume segments or subvolumes of amaximum volumetric region. The image data is output from image databuffer 28 to a display system 30 which generates a three-dimensionalimage of the region of interest from the image data for display on theimage display 62. The display system 30 includes a scan converter whichconverts sector scan signals from beamformer 20 to conventional rasterscan display signals. The display system 30 also includes a volumerenderer. A system controller 32 provides overall control of the systemin response to user inputs and internally stored data. The systemcontroller 32 performs timing and control functions and typicallyincludes a microprocessor and associated memory. The system controlleris also responsive to signals received from the control panel andtouchscreen display 36 through manual or voice control by the systemuser. An ECG device 34 includes ECG electrodes attached to the patient.The ECG device 34 supplies ECG waveforms to system controller 32 fordisplay during a cardiac exam. The ECT signals may also be used duringcertain exams to synchronize imaging to the patient's cardiac cycle.

FIG. 3 is a more detailed block diagram of an ultrasound system whenoperating with a matrix array for 3D imaging. The elements of thetwo-dimensional transducer array 14 of FIG. 1 are divided into Mtransmit sub-arrays 30A connected to M intra-group transmit processorsand N receive sub-arrays 30B connected to N intra-group receiveprocessors. Specifically, transmit sub-arrays 31 ₁, 31 ₂, . . . , 31_(M) are connected to intra-group transmit processors 38 ₁, 38 ₂, . . ., 38 _(M), respectively, which in turn are connected to channels 41 ₁,41 ₂, . . . , 41 _(M) of a transmit beamformer 40. Receive sub-arrays 42₁, 42 ₂, . . . , 42 _(N) are connected to intra-group receive processors44 ₁, 44 ₂, . . . , 44 _(N), respectively, which, in turn, are connectedto processing channels 48 ₁, 48 ₂, . . . , 48 _(N) of a receivebeamformer 20. Each intra-group transmit processor 38 _(i) includes oneor more digital waveform generators that provide the transmit waveformsand one or more voltage drivers that amplify the transmit pulses toexcite the connected transducer elements. Alternatively, eachintra-group transmit processor 38 _(i) includes a programmable delayline receiving a signal from a conventional transmit beamformer. Forexample, transmit outputs from the transmitter 10 may be connected tothe intra-group transmit processors instead of the transducer elements.Each intra-group receive processor 44 _(i) may include a summing delayline, or several programmable delay elements connected to a summingelement (a summing junction). Each intra-group receive processor 44 _(i)delays the individual transducer signals, adds the delayed signals, andprovides the summed signal to one channel 48 _(i) of receive beamformer20. Alternatively, one intra-group receive processor provides the summedsignal to several processing channels 48 _(i) of a parallel receivebeamformer. The parallel receive beamformer is constructed to synthesizeseveral receive beams simultaneously (multilines). Each intra-groupreceive processor 44 _(i) may also include several summing delay lines(or groups of programmable delay elements with each group connected to asumming junction) for receiving signals from several pointssimultaneously. A system controller 32 includes a microprocessor and anassociated memory and is designed to control the operation of theultrasound system. System controller 32 provides delay commands to thetransmit beamformer channels via a bus 53 and also provides delaycommands to the intra-group transmit processors via a bus 54. The delaydata steers and focuses the generated transmit beams over transmit scanlines of a wedge-shaped transmit pattern, a parallelogram-shapedtransmit pattern, or other patterns including three-dimensional transmitpatterns. A system controller 32 also provides delay commands to thechannels of the receive beamformer via a bus 55 and delay commands tothe intra-group receive processors via a bus 56. The applied relativedelays control the steering and focusing of the synthesized receivebeams. Each receive beamformer channel 48 _(i) includes a variable gainamplifier which controls gain as a function of received signal depth,and a delay element that delays acoustic data to achieve beam steeringand dynamic focusing of the synthesized beam. A summing element 50receives the outputs from beamformer channels 48 ₁, 48 ₂, . . . , 48_(N) and adds the outputs to provide the resulting beamformer signal toan image generator 30. The beamformer signal represents a receiveultrasound beam synthesized along a receive scan line. Image generator30 constructs an image of a region probed by a multiplicity ofround-trip beams synthesized over a sector-shaped pattern, aparallelogram-shaped pattern or other patterns includingthree-dimensional patterns. Both the transmit and receive beamformersmay be analog or digital beamformers as described, for example, in U.S.Pat. Nos. 4,140,022; 5,469,851; or 5,345,426 all of which areincorporated by reference.

The system controller controls the timing of the transducer elements byemploying “coarse” delay values in transmit beamformer channels 41 _(i)and “fine” delay values in intra-group transmit processors 38 _(i).There are several ways to generate the transmit pulses for thetransducer elements. A pulse generator in the transmitter 10 may providepulse delay signals to a shift register which provides several delayvalues to the transmit subarrays 30A. The transmit subarrays providehigh voltage pulses for driving the transmit transducer elements.Alternatively, the pulse generator may provide pulse delay signals to adelay line connected to the transmit subarrays. The delay line providesdelay values to the transmit subarrays, which provide high voltagepulses for driving the transmit transducer elements. In anotherembodiment the transmitter may provide shaped waveform signals to thetransmit subarrays 30A. Further details concerning the transmit andreceive circuitry of FIG. 3 may be found in U.S. Pat. No. 6,126,602.

FIG. 4 illustrates a two-dimensional matrix array transducer 70 whichscans a volumetric region 80. By phased array operation of thetransducer and imaging system described above, the matrix array can scanbeams over a pyramidal volumetric region 80. The height of the pyramidfrom its apex to its base determines the depth of the region beingimaged, which is chosen in accordance with factors such as the frequencyand depth of penetration of the beams. The inclination of the sides ofthe pyramid are determined by the degree of steering applied to thebeams, which in turn are chosen in consideration of the delays availablefor beam steering and the sensitivity of the transducer to off-axis(acutely inclined) beam steering.

A maximal volumetric region such as volumetric region 80 may be ofsufficient size to encompass the entire heart for 3D imaging as shown inFIG. 5, in which the heart 100 is shown being apically scanned. Threechambers of the heart 100 are shown in the heart graphic of FIG. 5,including the right ventricle (RA), the left atrium (LA), and the leftventricle (LV). Also shown is the aorta (AO) and its aortic valve 102,and the mitral valve 104 between the LA and the LV. However the timerequired to scan the entire maximal volumetric region 80 to visualizethe entire heart may be too slow for satisfactory real time imaging, ormay take too long such that motion artifacts occur, or both. Inaccordance with the principles of the present invention, the maximalvolumetric region is divided into subvolumes B (back), C (center) and F(front), as shown in FIG. 6. While the volumetric region 80 may subtendan angle in the azimuth (AZ) direction of 60°, for instance, thesubvolumes will subtend lesser angles.

In the embodiment of FIG. 6 the subvolumes each subtend an angle of 30°.This means that, for the same beam density and depth, each subvolume canbe scanned in half the time of the entire volumetric region 80. Thiswill result in a doubling of the real time frame rate of display. Thesubvolumes can be made contiguous or overlapping. For example, if theangle of the maximal volumetric region were 90°, three contiguoussubvolumes of 30° each might be employed. Alternatively, for a 60°maximal volumetric region, three 20° subvolumes could be used for aneven higher frame rate. In the embodiment of FIG. 6 the B and Fsubvolumes are contiguous in the center of the maximal volumetric region80 and the C subvolume is centered at the center of the region 80. Asexplained below, this partitioning of the region 80 provides a constant,easy-to-comprehend reference of the 3D volumes for the benefit of thesonographer.

In accordance with a further aspect of the present invention, each ofthe subvolumes is chosen by toggling a single control on the touchscreen68 of the ultrasound system, enabling the sonographer to move throughthe sequence of subvolumes without moving the probe. In cardiac imaging,locating an acceptable acoustic window of the body is often challenging.Since the heart is enclosed by the ribs, which are not good conveyors ofultrasound, it is generally necessary to locate an aperture through theribs or beneath the ribs for the probe. This is particularly difficultin 3D imaging, as the beams are steered in both elevation (EL) andazimuth. Once the sonographer finds an acceptable acoustic window to theheart, it is of considerable benefit to hold the probe in contact withthe window during scanning. In an embodiment of the present inventionthe sonographer can locate the acoustic window while scanning the heartin 2D in the conventional manner. Once an acceptable acoustic window hasbeen found during 2D imaging, the system is switched to 3D imaging withthe touch of a button; there is no need to move the probe. The user canthen step from the back to the center to the front subvolume with asingle button, observing each subvolume in live 3D imaging and withoutthe need to move the probe at any time.

FIG. 7 illustrates the profiles of each azimuthal center plane of eachof the B, C, and F subvolumes formed as described above. When the threesubvolumes are formed as illustrated in FIG. 6, these center planesuniquely correspond to each subvolume: the center plane of the backsubvolume B is a right triangle inclined to the left, the center planeof the front subvolume F is a right triangle inclined to the right andthe center plane of the center subvolume C is symmetrical. Asillustrated below, the shapes of these planes enable the sonographer toimmediately comprehend the subvolume being viewed. FIGS. 8 a, 8 b, and 8c illustrate screen shots taken of a display screen 62 when the threesubvolumes are displayed. In these and subsequent drawings the imageshave undergone black/white reversal from their conventional ultrasounddisplay format for clarity of illustration. As just explained, the Fsubvolume in FIG. 8 a is seen to be inclined to the right, the Bsubvolume in FIG. 8 c is inclined to the left, and the C subvolume inFIG. 8B is seen to be symmetrically balanced.

As a different subvolume is selected for viewing, the inclination of thebeam planes of the transmit and receive beams is changed to acquire thedesired subvolume. FIG. 9 a is a view normal to the plane of the matrixtransducer which illustrates the beam scanning space in the theta-phiplane for 3D scanning. In this beam scanning space a row of beams in ahorizontal line across the center of the aperture 90 extends normal tothe face of the transducer in elevation but are steered progressivelyfrom left to right from −45° to 0° (in the center) to +45° in azimuth,as the transducer is operated as a phased array transducer. Similarly, acolumn of beams in a vertical line down the center of the aperture 90extends normal to the face of the transducer in azimuth but are steeredprogressively from −45° to 0° (in the center) to +45° in elevation fromthe bottom to the top of the array. In FIG. 9 a a group of beam planesinclined from 0° to +30° is used to scan the front subvolume F. Eachelevational beam plane extends from −30° to +30° in azimuthalinclination in this illustrated embodiment. When probe is stepped toscan the center subvolume C the transmit beam planes extend from a −15°inclination to a +15° inclination as shown in FIG. 9 b. When the probeis stepped to scan the back subvolume B the transmit beam planes usedare those inclined from −30° to 0° as shown in FIG. 9 c. In each ofthese illustrations the beams in the beam plane are symmetricallyinclined in azimuth from −30° to +30°. However in a constructedembodiment other inclinations could be used and/or the subvolume couldbe inclined asymmetrically to the left or right in azimuth as desired.Since the selection of the transmit and receive beam inclinations isdone electronically by the system controller and the transmitter, thereis again no need to move the probe from its acoustic window when makingthis change.

In a linear array embodiment, in which all of the beams are normal tothe plane of the transducer, the transmit and receive apertures would bestepped along the array to transmit and receive spatially differentsubvolumes.

In a constructed embodiment 4× multiline is used to increase the beamdensity, which means that four receive beams are formed in response toeach transmitted beam. FIG. 10 shows a typical 4× multiline pattern, inwhich each transmit beam, T1 and T2 in this illustration, results infour receive beams represented by the four x's located around eachtransmit beam.

In accordance with another aspect of the present invention, each 3Dsubvolume display is also accompanied by two 2D images which help thesonographer orient the image being viewed. As previously explained, thesonographer begins by scanning the heart in 2D, moving the probe untilan appropriate acoustic window is found. In this survey mode ofoperation, the matrix array probe is transmitting and receiving a single2D image plane oriented normal to the center of the array. Once theacoustic window is found the 2D image is the center image plane of themaximal volumetric region 80 of FIG. 6. The user then touches the “3D”button on the touchscreen 68 to switch to 3D imaging, and a single 3Dimage appears on the screen. The user can then touch the “Image” buttonon the touchscreen to see a number of display options. In a constructedembodiment one of these buttons has three triangles on it (“3Δ”), andwhen this button is touched the display screen 62 shows the three imagesshown in FIG. 11, which is a B/W inverted actual screen shot. At the topcenter of the screen is the front subvolume F 3D image. At the lowerleft of the screen is a 2D image 110 of the face 110′ of the subvolumeF. When the three subvolumes are chosen as shown in FIG. 6, the image110 is also the center image of the maximal volumetric region 80 and isalso the guiding 2D azimuthal image plane used in the initial 2D surveymode. On the lower right side of the display is a 2D image 112 of thecenter cut plane of the subvolume F, which is an elevation referenceimage in the illustrated embodiment. It is seen that the image 112 bearsthe distinctive profile of the front subvolume discussed in conjunctionwith FIG. 7. Thus these orthogonal 2D images 110 and 112 providefamiliar 2D assistance to the user in comprehending the orientation ofthe 3D subvolume image F. The subvolume F is the subvolume subtended bythe dashed lines extending from the matrix array transducer 70 throughthe heart graphic 100 in FIG. 11 a.

Also on the touchscreen 68 at this time is a button denoted “Front”, forthe F image view. When the user touches this button, it changes to a“Center” button and the display of FIG. 12 appears on the display screen62. The display has now switched to the 3D center subvolume C at the topof the screen. The 2D image 110 is an image of the center cut plane ofthis subvolume from the near side to the far side of the subvolume C asindicated by 110′. The symmetrical 2D image 114 is the distinctivesymmetrical cut plane through the center of the subvolume from left toright. The subvolume C is that subtended by the dashed lines extendingfrom the matrix transducer 70 in FIG. 12 a through the heart graphic100.

When the Center button is touched again it changes to read “Back” andthe image display of FIG. 13 appears with the 3D subvolume B shown atthe top of the display. The 2D image 110 is still the center plane ofthe maximal volume in this embodiment (FIG. 6), and is also the faceplane on the right side 110′ of the subvolume B. The distinctive centercut plane from left to right through the subvolume B is shown at 116.The volumetric subregion shown in this display is the region subtendedby the dashed lines extending from the matrix transducer 70 in FIG. 13 athrough the heart graphic 100.

Continual touching of the Front/Center/Back button will continue toswitch the display through these three image displays. The sequence ofthe images may be selected by the system designer. For instance, in aconstructed embodiment, the initial image display is of the Backsubvolume and the selection switch toggles the display through theBack/Center/Front views in sequence. Thus, the sonographer can visualizethe entire heart in live 3D by stepping through the three high framerate subvolumes in succession.

In each of the image displays of FIGS. 11-13 the viewing perspective ofthe live 3D subvolume can be adjusted by the user. The images initiallyappear in the perspectives seen in the drawings but can then by changedby the user by rotating the trackball on the control panel 66. As thetrackball is manipulated the 3D subvolumes appear to rotate in thedisplay, enabling the user to view the anatomy in each subvolume fromthe front, back, sides, or other rotated viewing perspectives. This isaccomplished by changing the dynamic parallax rendering look directionin response to movement of the trackball.

In accordance with a further aspect of the present invention, the 3Dimage orientation may be varied in accordance with the preferences ofthe user. For example, adult cardiologists usually prefer to visualizean apical view of the heart with the apex of the heart and the apex ofthe image both at the top of the screen as shown in the preceding FIGS.11-13. In this orientation the heart is essentially seen in an upsidedown orientation. Pediatric cardiologists, on the other hand, willusually prefer to view both the apex of the heart and the apex of theimage at the bottom of the screen, in which the heart is viewed in itsright side up anatomical orientation. To enable each user to view theheart as he or she is accustomed, an embodiment of the present inventionwill have an Up/Down Invert button. In the embodiment described belowthe ultrasound system also has a Left/Right Reversal button which isalso described.

When the user touches the Up/Down Invert button on the touchscreen 68,the order in which the scanlines are processed for display in scanconversion and 3D rendering is reversed and the display will switch tothat shown in FIG. 14. In this view the 3D subvolume F has becomeinverted with the apex of the heart at the bottom of the image asillustrated by the matrix array 70 and the heart graphic 100 in FIG. 14a. The center plane 210 of the maximal volumetric region 80 has alsobeen correspondingly inverted and still illustrates the view of the face210′ of the inverted subvolume F. Likewise, the distinctive center cutplane 212 of the subvolume F is also inverted. Inversion of the imagealso reverses the left-right direction of the images on the displayscreen so that the original sense of the anatomy is retained in theimages. In the illustrated embodiment inversion (and reversal, asdiscussed below) will cause the “Back” subvolume to become the “Front”subvolume, and vice versa.

Touching the touchscreen button now reading Front will cause the buttonto change to Center and the display to switch to the inverted 3D centersubvolume C as shown in FIG. 15. The 2D front-to-back center plane 210of the subvolume C is inverted, as is the distinctive left-to-right cutplane 212. The subvolume C is that acquired between the dashed linesextending from the matrix array transducer 70 through the heart graphic100 in FIG. 15 a.

Touching the touchscreen button again will cause the button to change toBack and the display to change to that shown in FIG. 16. The inverted 3Dsubvolume B is that acquired as illustrated by the dashed linesextending from the matrix transducer 70 through the heart graphic 100 inFIG. 16 a. The 2D center plane 210 is the side face 210′ of the invertedsubvolume in this embodiment, and the distinctive cut plane 212 of thesubvolume B is also inverted.

In accordance with a further aspect of the present invention, theleft-right direction of the 3D images can also be reversed. When theLeft/Right Reversal button on the touchscreen 68 is touched, the orderof the scanlines used in the scan conversion and rendering displayprocesses is reversed, causing the images to change sense from left toright. This effectively causes front to become back, and vice versa forthe 3D subvolumes. For instance, FIG. 17 shows a 3D subvolume F afterleft/right reversal. The subvolume is viewed as if the direction of theanatomy has been reversed as illustrated by the reverse image 100′ ofthe heart in FIG. 17 a. The center plane 210 and the distinctive cutplane 312 in FIG. 17 are correspondingly reversed in display linesequence.

Sequencing through the Front/Center/Back button sequence will next causea reversed 3D subvolume C image to appear as shown in FIG. 18, as wellas reversed center plane image 310 and left to right cut plane 312. Theimage reversal is indicated by the reversed heart graphic 100′ in FIG.18 a. When the touchscreen button is touched a third time a reversed 3Dback subvolume image B appears as shown in FIG. 19, together withreversed center plane image 310 and back cut plane image 312. The imagesare oriented as though the heart were reversed as shown in FIG. 19 a.

Finally, the Up/Down Inverted images can also be Left/Right Reversed asshown in FIGS. 20, 21, and 22 for the front, center and back subvolumes.In this sequence the heart appears as if both inverted and reversed asshown by the heart graphic 100′ in FIGS. 20 a, 21 a, and 22 a. With bothup/down inversion and left/right reversal the object being scanned canbe viewed from any orientation, as if the user were scanning the anatomyfrom different perspectives of the body.

The aforedescribed embodiments effectively step the sonographer throughincrementally positioned subvolumes of the maximal volumetric region.Rather than step through a series of discretely positioned orientations,it may be desirable to continuously change the orientation of asubvolume. This is done by touching the “Volume Steer” button on thetouchscreen 68 when the user is in the 3D mode. In the volume steer modethe user can manipulate a continuous control on the control panel 66such as a knob or trackball to sweep the displayed volume back andforth. In a constructed embodiment one of the knobs below thetouchscreen 68 is used as the volume steer control, and a label on thetouchscreen above the knob identifies the knob as the volume steercontrol. When the system enters the volume steer mode, the 3D subvolumeshown on the screen can be reoriented with the control knob. When thevolume steer knob is turned to the right the displayed subvolume appearsto swing to the right from its apex, and when the knob is turned to theleft the displayed subvolume appears to swing to the left. A subvolumecan be steered in this manner in inverted, uninverted, reversed orunreversed viewing perspective. The motion appears continuous,corresponding to the continuous motion of the knob.

The control sequence for this continuous mode of volume steering isshown in the flowchart of FIG. 23. While the system is in this mode thesystem controller is continually monitoring any change in the volumesteer knob. If no movement is sensed, this monitoring continues as shownin step 501. If a change in the knob position is sensed (“Yes”), thecontroller checks in step 502 to see if the subvolume is at a limit ofthe maximal volumetric region over which volume steering is permitted(e.g., in contact with a side of maximal volume 80.) If the subvolumehas been steered to its limit, the system goes back to monitoring for achange in knob position, as only a knob change in the other directionwill swing the subvolume. If a limit position has not been reached, thebeam steering angles for the transmit and receive beamformers areincremented in accordance with the change in knob position to steer thevolume in the slightly different orientation in step 503. This volumegeometry change is communicated to the scan converter of the displaysystem in step 503 so that the newly acquired volumetric images will beshown in their new orientation. The beamformer controller computes thefirst beam position of the new volumetric orientation and the stop andstart orientations of the beams in step 504. The parameters for scanconversion to the new orientation are reset in step 505. The new beamparameters for the transmit and receive beamformers are set in step 506.The system then commences to acquire and display the 3D subvolume in itsnew orientation such as that shown in the screen shot of FIG. 24, andthe system controller resumes monitoring of the volume steer controlknob for a subsequent change. With this mode of operation thesonographer can electronically sweep a 3D subvolume back and forth overthe range limits of the maximal volumetric region to acquire high framerate 3D images within the maximal volumetric region without the need tomove the probe from its acoustic window. In a constructed embodimentsubvolumes subtending angles as great as 57° have been swept over amaximal volumetric region subtending as much as 90°.

1. An ultrasonic diagnostic imaging system for three dimensional imagingcomprising: a matrix array transducer which is operable to scanelectronically steerable beams over a volumetric region of a body; animage processor coupled to the matrix array transducer for producing 2Dand 3D images of a subvolume of the volumetric region; and a displaycoupled to the image processor which displays a live 3D image of thesubvolume region, a 2D image of a first plane of the subvolume region,and a 2D image of a second plane of the volumetric region which isorthogonal to the first plane and exhibits a profile identifying thesubvolume.
 2. The ultrasonic diagnostic imaging system of claim 1,wherein the display further comprises a display coupled to the imageprocessor which displays a live 3D image of the subvolume region, a 2Dimage of a face of the subvolume region, and a 2D image of a central cutplane of the subvolume region which is orthogonal to the face.
 3. Theultrasonic diagnostic imaging system of claim 1, wherein the displayfurther comprises a display coupled to the image processor whichdisplays a live 3D image of the subvolume region, a 2D image of a firstcentral cut plane of the subvolume region, and a 2D image of a secondcentral cut plane of the subvolume region which is orthogonal to thefirst cut central cut plane.
 4. The ultrasonic diagnostic imaging systemof claim 1, wherein the display further comprises a display coupled tothe image processor which displays a live 3D image of the subvolumeregion, a live 2D image of a face of the subvolume region, and a live 2Dimage of a central cut plane of the subvolume region which is orthogonalto the face.
 5. The ultrasonic diagnostic imaging system of claim 1,wherein the display further comprises a display coupled to the imageprocessor which displays a live 3D image of the subvolume region, a live2D image of a first central cut plane of the subvolume region, and alive 2D image of a second central cut plane of the subvolume regionwhich is orthogonal to the first cut central cut plane.
 6. Theultrasonic diagnostic imaging system of claim 1, further comprising auser control coupled to the image processor and responsive tomanipulation by a user to vary the viewing perspective of the live 3Dimage of the subvolume region.
 7. The ultrasonic diagnostic imagingsystem of claim 1, wherein the plane of the 2D image of the first planeof the subvolume region is oriented normal to the plane of the arraytransducer.
 8. The ultrasonic diagnostic imaging system of claim 7,wherein the plane of the 2D image of the second plane of the subvolumeregion is oriented normal to the plane of the array transducer.
 9. Theultrasonic diagnostic imaging system of claim 1, wherein the 2D image ofthe first plane of the subvolume region is in an azimuthal plane of thearray transducer and wherein the 2D image of the second plane of thesubvolume region is in an elevational plane of the array transducer. 10.A method for scanning and displaying a volumetric region of a bodycomprising: scanning a subvolume region of a body with electronicallysteerable beams from a matrix array transducer; image processing signalsreceived in response to the beams by volume rendering a live 3D image ofthe subvolume region; image processing signals received in response tothe beams by scan converting first and second 2D images of two planes ofthe subvolume region; and displaying concurrently the live 3D image andthe two 2D images of the subvolume region, wherein one of the 2D imagesexhibits a profile which identifies the subvolume.
 11. The method ofclaim 10, further comprising varying the viewing perspective of thedisplayed live 3D image with a user control.
 12. The method of claim 10,wherein image processing signals received in response to the beams byscan converting further comprises scan converting first and second 2Dimages of two orthogonal planes of the subvolume region.
 13. The methodof claim 12, wherein image processing signals received in response tothe beams by scan converting further comprises scan converting first andsecond 2D images of two orthogonal planes of the subvolume region whichare normal to the plane of the array transducer.
 14. The method of claim10, wherein image processing signals received in response to the beamsby scan converting further comprises scan converting a first 2D image ofa face of the subvolume region and scan converting a second 2D image ofa cut plane of the subvolume region.
 15. The method of claim 14, whereinthe cut plane of the subvolume region is orthogonal to the plane of thefirst 2D image.
 16. The method of claim 10, wherein image processingsignals received in response to the beams by scan converting furthercomprises scan converting a first 2D image of a first cut plane of thesubvolume region and scan converting a second 2D image of a second cutplane of the subvolume region.
 17. The method of claim 16, wherein thecut planes of the subvolume region comprise central cut planes.
 18. Themethod of claim 17, wherein the cut planes are orthogonal to each other.